There exists a variety of fabrics today which are capable of acting as a barrier to particulate matter, water and other liquids yet which allow water vapor and air to pass therethrough. Such fabrics are commonly referred to as "breathable barriers." Breathable barrier fabrics have been employed in outdoor fabrics, tarpaulins, garments, personal care products, infection control products, as well as numerous other articles. Moreover breathable barrier fabrics are often preferred over non-breathable barrier materials since breathable barrier fabrics allow moisture trapped beneath the fabric to escape as water vapor. Thus, apparel using breathable barrier fabrics is generally more comfortable to wear since the migration of water vapor through the fabric helps to reduce and/or eliminate discomfort resulting from excess moisture trapped against the skin.
While a variety of breathable barrier fabrics are known in the art, one particularly useful breathable barrier comprises stretched filled microporous films. Such films are typically filled with particles or other matter and then crushed or stretched to form a fine pore network which creates tortuous paths through the film. The film pore network allows gas and water vapor to pass through the film while acting as a barrier to liquids and particulate matter. The amount of filler within the film and the degree of stretching is controlled so as to create a network of micro pores of a size and/or frequency to impart the desired level of breathability to the fabric. An exemplary stretched filled film is described in commonly assigned WO Patent Application 95/16562 to McCormack which discloses a stretched filled film comprising a predominantly linear polyolefin polymer, a bonding agent and about 30 to 80% by weight calcium carbonate. The filled polyolefin film can be stretched to impart breathability to the film. The stretched film may then be laminated to a nonwoven web to create a laminate that takes advantage of the strength and integrity of the nonwoven web and the barrier properties of the stretched film.
Thin films, such as those that may result from the stretching or orienting of filled films, are often easily split or torn in the direction of orientation. Thus, as indicated above, stretched-filled films are often laminated to a support layer in order to provide additional strength and integrity to the film. The peel strength of the laminate is desirably strong enough to resist delamination which may result from further processing, transportation and/or storage of the laminate. Often this includes exposure to hot and humid conditions. Moreover, the laminate desirably also resists delamination which may result from mechanical stress applied to the laminate in use. As an example, wear of garments or diapers incorporating the barrier laminate subjects the laminate to stress as a result of abrasion, pulling and other manipulation of the article. In addition to the strain naturally resulting from wear, many articles today employ various fasteners, such as tape or hook and loop systems, which pull on the outer layer thereby creating additional strain on the laminate. Examples of fastening systems are disclosed in commonly assigned U.S. Pat. No. 5,605,735 to Zehner et al.; U.S. Pat. No. 5,019,073 to Roessler et al.; U.S. Pat. No. 5,624,429 to Long et al.; and U.S. patent application Ser. No. 08/534,227 filed Sep. 26, 1995 to Roessler et al. As a result of the pull created by fasteners, many nonwoven/film laminates begin to peel or delaminate, thereby causing the film to separate from the support fabric. In this regard the film becomes considerably more prone to being split or torn once separated from the support fabric. Delamination may therefore ultimately result in a loss of barrier properties, i.e. a leaky product. In addition, even when delamination occurs in areas where the barrier properties are less critical, for example along the edges of a product, the delamination is aesthetically undesirable and gives the appearance of a product of lesser quality. Therefore, breathable barrier laminates having good peel strength are highly desirable.
However, lamination of thin breathable films to one or more supporting layers in a manner to achieve the desired peel strength is particularly difficult without degrading either the barrier properties and/or the breathability of the films. Generally speaking, when thermally bonding two layers of thermoplastic materials together, better lamination or peel strengths may be achieved by increasing the bonding temperature and/or by increasing the overall bond area. Thermal bonding of thin films and a support layer at temperatures necessary to achieve increased peel strengths often create "burn throughs" or pinholes in the film which degrade the barrier properties. This is of course highly undesirable in fabrics where the film is intended to act as a barrier to materials such as urine and other body exudates and an even greater concern where the film is employed as a barrier to hazardous materials such as, for example, blood. In addition, point bonding often destroys the breathability of the fabric within the bond areas, and thus increasing the overall bond area can undesirably lower the breathability of the laminate. Extensive thermal bonding can also undesirably decrease the hand and flexibility of the resulting laminate. Moreover, adhesive lamination of the thin breathable film and support fabric may often likewise suffer from delamination as a result of the physical and mechanical stress experienced by breathable barrier laminates. Furthermore, certain adhesives can decrease the breathability of the laminate and/or undesirably stiffen the laminate.
Thus, there exists a need for a breathable barrier laminate which exhibits good breathability and barrier properties yet which also exhibits excellent peel strength. Moreover, there exists a need for such a breathable barrier laminate which has good hand, is durable and further which may employ a variety of film and laminate structures. Further, there exists a need for such a breathable barrier laminate that may be fabricated by a robust process which is functional under a wide latitude of processing conditions and parameters.